The detection and measurement of hydrogen sulphide
Gas measurement techniques for hydrogen sulphide (H2S) have been investigated, with particular reference to the monitoring of average ambient concentrations and also the rapidly changing concentrations which may be associated with vehicle pollution. Two new techniques have been identified, and new equipment built and tested, for H2S determination. The first of these is designed to measure long term average concentrations of H2S and the second to evaluate rapidly changing peak concentrations over very short periods of time. The implementation of catalytic converters in modern petrol driven motor vehicles has resulted in undesirable emissions of hydrogen sulphide gas. The reasons for these emissions are discussed. Ambient concentrations of H2S have been measured at the roadside and the average contribution originating from vehicular emissions on major roads determined. Results are presented which confirm the elevation of hydrogen sulphide concentrations at the road side of an average of single figure parts per billion. Peak H2S concentrations of up to 100 ppb were also measured at the roadside and within motor vehicles. The peaks were of very short duration and therefore of only minimal contribution to average ambient concentrations. Measurements of H2S concentrations at a variety of locations have also been made,and results are presented, of comparisons between areas with no source of H2S nearby, roadside sites and other possible H2S sources such as sewage treatment works and landfill sites. Known H2S concentrations, in excess of 500 ppm from a point source on a landfill site, were found to diminish rapidly toward zero, within 150 m of the source. This demonstrated the high reactivity of H2S and therefore the importance of measuring H2S concentration as closely as possible to the emission source. Consequently, this high reactivity is particularly important in the consideration of roadside and 'on-road' monitoring of H2S.